1. Field of Invention
This invention relates to a continous process for preparing a multiblock copolymer of two monomers such as styrene and butadiene, butadiene and isoprene, etc. More specifically this invention relates to the continous process of producing such multiblock copolymer by alternate feeding of the respective monomers into the continous polymerization system.
2. Related Prior Art
The preparation of block copolymers is generally effected in batch systems. In such cases the reaction is initiated with one monomer, together with diluent and catalyst in the reactor, and polymerization continued until that monomer has been completely polymerized to form the initial block. Then the second monomer is introduced and polymerization continued until that monomer is completely polymerized to form the second block, following which more of the first monomer is introduced to form the third block, etc.
Since it is considered necessary to have the system completely purged of one monomer before introducing the other, either by completing polymerization or by removal of unpolymerized monomer, it had not been considered that such multiblock copolymers could be produced by a continuous system.
British Pat. No. 1,160,234 is typical of the prior art in which a block copolymer of butadiene and isoprene is prepared in a batch operation. There is no mention of a continuous process for preparing the three block copolymer described therein.
U.S. Pat. Nos. 3,231,635 and 3,265,765 are typical prior art disclosures relating to the batch production of block copolymers of styrene and butadiene.
U.S. Pat. No. 3,198,774 discloses a continuous process for preparing block copolymers of butadiene and styrene using an alkyl halide to prevent gelation and reactor plugup. However patentees feed the butadiene and styrene simultaneously with the result that of the 22.6 percent styrene found in the resultant copolymer only 13.8 percent (based on total polymer content) is in the form of block copolymer.